1. Field of the Invention
This invention is directed to an injection valve typically used in conjunction with an injection well. Injection wells are drilled for example in close proximity to hydrocarbon producing wells that have peaked in terms of their output. Fluid for example water is pumped under pressure into an injection well to maintain the pressure of the underlying formation as the well is produced. Injected water acts to force the hydrocarbons into adjacent producing wells thus increasing the yield.
2. Description of Related Art
U.S. Pat. No. 7,866,401 discloses an injection safety valve having a restrictor, also known as an orifice, create a pressure differential so as to move a flow tube past a flapper valve. The diameter of the restrictor is fixed.
A problem with injection valves is a phenomenon known to those of normal skill in the art as “chattering”. Chattering occurs when the injection rate is insufficient to allow the valve to fully open, whereby the flow across the fixed orifice (the standard in injection valves) is too low to compress the power spring and shift the flow tube into a position to hold the flapper into the fully open and protected position.
Chattering causes the flapper to intermittently and rapidly slam into the flapper seat causing premature failure of either the flapper and/or seat. Such failure can cause an unsafe well condition necessitating premature, immediate shut in of the well, and expensive well remediation,—sometimes costing tens of millions of dollars in the instance of subsea wells.